Optical systems and circuits require a variety of devices incorporating optical structures. For example, optical amplifiers may be used in long-haul optical fiber communication systems. Alternatively, optical amplifiers may serve as a pumping source for fiber amplifiers. For these applications optical amplifiers that provide high output power are particularly attractive. High power is achieved by increasing the total electrical power applied to the amplifier, which requires that the amplifier have a large lateral dimension.
A number of optical amplifiers are known which have an increased lateral dimension. Such amplifiers include broadarea structures, tapered passive waveguides for adiabatic beam expansion (see, for example, Koren et al., "High-power laser amplifier photonic integrated circuit for 1.48 micron wavelength operation," Appl. Phys. Lett., vol. 59, pp. 2351-2353, 1991) and tapered active region devices (see, for example, Yazaki et al., IEEE Photon Tech. Lett., 3, 1060, 1991; and Walpole et al., "High-power strained-layer InGaAs/AlGaAs tapered traveling wave amplifier," Appl. Phys. Lett., vol. 61, pp. 740-742, 1992). For example, Koren et al. discloses a 1.48 micron integrated laser/amplifier device having a continuous-wave (CW) output power of up to 0.37 W. By providing a tapered amplifier without lateral guiding and widths up to 250 microns CW output powers of 1-2 W have been achieved. Additionally, a short-wavelength tapered amplifier operating at 0.98 microns has been shown to provide 3.1 W of CW output power (see J.N. Walpole et al., "High Power tapered semiconductor amplifiers and lasers at 980 nm," in Proc. Conf. IEEE/LEOS Annu. Meeting, Boston, Mass., paper PD2, Nov. 1992.).
Tapered optical amplifiers provide a number of advantages over other types of optical amplifiers. For example, such amplifiers provide high saturation power, suppression of backward-amplified spontaneous emission, and reduced sensitivity to facet reflection. However, there are also a number of drawbacks associated with tapered amplifiers and large laterally dimensioned semiconductor amplifiers generally. These difficulties arise from the lack of lateral waveguiding control and include such problems as the inability to efficiently couple the amplifier output, which is distributed over a relatively large area, into a single-mode fiber.
Accordingly, it is desirable to provide a semiconductor amplifier having a large lateral dimension for supplying high output power in which the lateral waveguiding of the optical power can be controlled.